This invention relates to a method of operating a heat pump in a reverse mode for a short period of time at start-up to eliminate flooded starts.
Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments to be conditioned. In a typical refrigerant system operating in the cooling mode, a refrigerant is compressed in a compressor and delivered to a condenser (or outdoor heat exchanger in this case). In the condenser, heat is exchanged between outside ambient air and the refrigerant. From the condenser, the refrigerant passes to an expansion device, at which the refrigerant is expanded to a lower pressure and temperature, and then to an evaporator (or indoor heat exchanger). In the evaporator heat is exchanged between the refrigerant and the indoor air, to condition the indoor air. When the refrigerant system is operating, the evaporator cools the air that is being supplied to the indoor environment.
The above description is of a refrigerant system being utilized in a cooling mode of operation. In the heating mode, the refrigerant flow through the system is essentially reversed. The indoor heat exchanger becomes the condenser and releases heat into the environment to be conditioned (heated in this case) and the outdoor heat exchanger serves the purpose of the evaporator and exchangers heat with a relatively cold outdoor air. Heat pumps are known as the systems that can reverse the refrigerant flow through the refrigerant cycle in order to operate in both heating and cooling modes. This is usually achieved by incorporating a four-way reversing valve or an equivalent device into the system schematic downstream of the compressor discharge port. The four-way reversing valve selectively directs the refrigerant flow through the indoor or outdoor heat exchanger when the system is in the heating or cooling mode of operation respectively. Furthermore, if the expansion device cannot handle the reversed flow, than a pair of expansion devices, each along with a check valve, are employed instead.
A typical problem with the heat pumps is the occurrence of a “flooded start.” Since refrigerant migrates to the coldest spot within the system, after system's shutdowns, a significant amount of liquid refrigerant may be accumulated in the evaporator. The evaporator would be the indoor heat exchanger in the cooling mode, and the outdoor heat exchanger in the heating mode. When the system is again started, this liquid refrigerant is ingested into the compressor, which is undesirable for several reasons the most important of which are related to permanent damage of compressor elements, subsequent potential refrigerant circuit contamination and prolonged period of downtime. The flooded start also results in on objectionable noise on compressor start-up.
One method to address flooded starts is the provision to install an accumulator attached to the compressor suction line. However, accumulators would only partly solve the problem since they would only store a limited amount of refrigerant. Accumulators also carry additional system expense and would often be a source of potential refrigerant leaks. Thus, a simpler, less expensive and more reliable solution to eliminate flooded starts would be desirable.